During the last forty years, researchers and therapists have been actively involved in designing improved methods for measuring the amount of angular rotation between two human body portions connected to a common joint. In an article entitled "Measurement Of Joint Motion," found in Archives of Physical Medicine, pages 416-423, July, 1945, Catherine West discusses an instrument consisting of a large protractor which can be used to measure the range of motion associated with a body joint. In using the protractor, one would align the axis of a joint with the center of the protractor. By noting the initial and final protractor readings, one could subjectively determine the angular displacement between the two body portions.
An improvement on this instrument is disclosed in an article written by M. D. Moore entitled "The Measurement Of Joint Motion, Part III: Technique of Goniometry," found in Physical Therapy Review, Volume 29, pages 256-264, June, 1949. Moore discloses a goniometer which is designed to utilize the anatomical zero point as a starting position for all measurements. In this device, the stationary arm of the instrument is aligned with the proximal portion of a limb, while the moving arm of the instrument is aligned with the distal portion. While the Moore instrument is an improvement over the West protractor, both of the devices suffer from the difficulty in subjectively aligning the instrument with the body portions.
An article entitled "A Simple Objective And Reliable Measure of Flexibility," by Jack Leighton and published in Research Quarterly, Volume 13, pages 205-216, May, 1942, discloses a measuring instrument which can be strapped directly to the body portions, thereby avoiding the need to subjectively align the instrument. The instrument consisted of a 360.degree. dial and an associated weighted pointer connected to one body portion. The total range of motion of the one body portion moving against gravity was recorded on the dial. Although this instrument was capable of measuring the range of motion associated with a joint by starting from the extreme position in one direction and ending at the terminal point of movement in the other direction, it was not capable of measuring single joint flexion or extension from the anatomical zero point.
Peter V. Karpovich, in Physiology Of Muscular Activity, Philadelphia: W. B. Saunders Company, 1965, on page 38 discusses an electro-goniometer which provides a continual recording to the angular displacement between two body portions connected to a common joint. The electro-goniometer utilizes a potentiometer for measuring the angular position between the two body portions. One of the problems associated with this instrument is the fact that the instrument is supported on the body portions in such a manner which may alter normal movement of the body portions which typically requires torsion and cross plane motion.